1. Field of the Invention
The invention relates to an alarm mat laid on a floor surrounding a dangerous area not to be accessed in, for example, plants and construction sites.
2. Description of the Related Art
Japan Patent No. 2751659 (hereinafter, called prior art 1) discloses an alarm mat provided with a large number of semispherical projections provided on a base plate including a plywood board, sealed tubular members formed in a bellows-like shape in cavities of the projections, and whistles sounded by air inflow and outflow to and from the sealed tubular members. This alarm mat needs no power supply.
Japan Patent No. 2903854 (hereinafter, called prior art 2) discloses an alarm mat provided with a large number of semispherical projections elastically deformable and provided on a base plate including a plywood board, sealed tubular members formed in the projections, whistles sounded by the deformation of the sealed tubular members, and a protective member surrounding lower parts of the sealed tubular members. This alarm mat too needs no power supply.
Japan Utility Model Registration No. 3102048 (hereinafter, called prior art 3) discloses an alarm mat having an elastic plate having cavities and through holes formed therein, air-permeable sponges filling the cavities, and reed whistles fitted in the through holes.
The prior arts 1 and 2, wherein it is necessary to set the sealed tubular members and the whistles in a large number of projections, requires extensive man-hours during the production of these mats, leading to a time-consuming production process and large production costs. According to the prior art 3, a degree of elastic deformation when the alarm mat is stepped on by foot is rather small as compared to a large volume in total of the cavities formed in the elastic plate. This structural disadvantage involves the risk that airflow leaking from the cavities through the whistles is possibly too weak to make the whistles produce sound. The prior art 3 has another disadvantage that the elastic plate where the cavities are formed has a large area. Such a large plate, when stepped on by foot, does not immediately regain its original shape, therefore, there are times when the whistles fail to produce sound.